When Washington's ambassador to Tunis dined at Mohamed Sakher el-Materi's beachside home in July 2009, his eyes nearly popped out.

While ordinary Tunisians struggled with rising food prices, the powerful young business magnate served up a feast of steak, turkey and octopus followed by ice cream flown in from Saint Tropez. A caged pet tiger living in the garden on a daily diet of four chickens reminded the ambassador of Uday Hussein's lion cage in Baghdad.

But the decadence was not a complete surprise. Materi had married Zine al-Abidine Ben Ali's daughter, and in an earlier cable back to the US, obtained by WikiLeaks, the ambassador wrote: "President Ben Ali's extended family is often cited as the nexus of Tunisian corruption."

Such suspicions seemed not to matter to the British government and the Duke of York, however. Just over a year later, the 29-year-old Tunisian was sitting down to eat again, this time in Buckingham Palace at a lunch arranged for him by the Queen's second son. The function was part of Prince Andrew's duties as the government's special trade representative. Materi was joined by around 15 bosses from British multinationals.

Only three months later, the Ben Ali regime was overthrown, Materi fled, and he is now under investigation for money laundering. This weekend the judgment of both Prince Andrew and his political masters is being severely questioned.

Other meetings and lunches held by the duke with Colonel Gaddafi and other senior figures in the Libyan regime have only added to the pressure and the instability sweeping through the Middle East is exposing his network of autocratic contacts.

Andrew was appointed as the UK's special representative for international trade and investment in 2001. He carried out 550 engagements in 2009, with many focused on autocratic regimes and developing countries in the Middle East, central Asia and the far east. The role is unpaid, but the duke travels in style and with an entourage. His globetrotting cost the taxpayer more than £500,000 in hotels and flights in the year to April 2010.

Palace records show that in the last year the duke courted deals for UK firms with the prime minister of Bahrain, the prime minister of Kuwait and the deputy prime minister of Qatar and held meetings with the Saudi Arabian defence minister and a Jordanian prince with a senior role in the country's military.

"He is sent to take specific issues to people there," said his spokesman. "It is because he is a member of the royal family that doors are open to him in the Middle East and developing economies that are not open to others. It works less well in more mature economies such as France and Sweden. By opening the door he can let the president or crown prince know about a problem for a company that he didn't know previously existed. It sorts out problems further down the chain."

Andrew is briefed by British business leaders to lobby for their interests with foreign leaders. The court circular reveals recent meetings with Robert Dudley, the chief executive of BP, and Tom Albanese, the chief executive of Rio Tinto. He received William McKeeva, the president of the Cayman Islands tax haven, at the Royal Lodge in Windsor and met the emir of Qatar at Buckingham Palace.

He regularly met defence contacts too. He travelled to Riyadh to meet Prince Khalid bin Sultan bin Abdul Aziz Al Saud, the Saudi Arabian defence minister, and held meetings at the Farnborough air show with Prince Feisal Ibn Al Hussein, special assistant to the chairman of the Jordanian joint chiefs of staff, as well as the defence ministers of India and Malaysia.

But he has repeatedly caused controversy. Sir Ivor Roberts, former ambassador to Italy, Yugoslavia and Ireland, this week said the duke was rude to foreign dignitaries and "brusque to the point of rudeness", while Simon Wilson, Britain's former deputy head of mission in Bahrain has branded him boorish.

Tatania Gfoeller, Washington's ambassador to Kyrgyzstan, recorded how, speaking at a business event, Andrew called the UK's Serious Fraud Office "idiots" for investigating bribery claims around an arms deal in Saudi Arabia.

But many in government and business see him as a secret weapon who drums up business for UK plc in a way others cannot.

"He was a definite net asset," said a former diplomat who worked with the duke in the Middle East. "He is not the greatest intellectual but when he is in a good mood and pointed in the right direction he is good with Middle East businessmen and minor royals. He works extremely hard and takes it all very seriously. He doesn't drink and is very energetic. There were flashes of his father's temper and he can be very stubborn. It was usually when he was tired and tried to do too much. He required careful handling, You had to be respectful, but firm."

"The Duke of York has made a valuable contribution to British business," said a spokesman for UK Trade and Investment, the government export agency which employs him most. "Many who have worked with the duke believe he is a real asset to supporting UK business success. He promotes UK business interests abroad and helps to attract inward investment."